Process and apparatus for eliminating the excentricity
effect of rollers in hot and cold rolling
mills for metal sheets



CITY

y 1967 K. NEUMANN ETAL PROCESS AND APPARATUS FOR ELIMINATING THE EXCENTRI EFFECT OF ROLLERS IN HGT AND COLD ROLLING MILLS FOR METAL SHEETS Filed Aug. 26, 1963 United States Patent 3,331,229 PROCESS AND APPARATUS FOR ELIMINATING THE EXCENTRICITY EFFECT OF ROLLERS IN HOT AND COLD ROLLING MILLS FOR METAL SHEETS Karl Neumann, Hans Siegfried Mctzger, and Karl Glawe,

St. Inghert, Saar, Germany, assignors to Verwaltungsgesellschaft, Moeller u. Neurnann, oifene Handelsgesellschaft, St. Inglbert, Saar, Germany Filed Aug. 26, 1963, Ser. No. 305,241 Claims priority, application Germany, Aug. 29, 1962, V 22,969 11 Claims. (Cl. 72-8) This invention relates to a process and apparatus for eliminating the excentricity effect of the rolls in hot and cold rolling mills for metal sheets and strips, and more particularly to a process and apparatus of this type in which a separate recording or registering device is associated with the rolling mill for scanning the excentricity of the rolls and for transmitting to roll adjusting devices signals corresponding to the excentricity characteristics.

The problem of the influence of non-round or excentric rollers in hot and cold rolling mills for metal sheets and strips is well known. Still it is not possible to produce the heavy back-up rolls of four-high stands usually employed in sheet metal rolling mills, completely without beat or excentricity. The amount of excentricity in the case of rolls for cold rolling operations is actually only a few hundreds of a millimeter, but this proves to be a very disturbing factor in view of the present day requirements for exact tolerances of thin metal sheets and strips.

The elimination of the influence of excentric rollers by means of control arrangements has been described as being too expensive. But in contrast to this viewpoint the present invention shows a way of solving this problem by means of a control arrangement in a manner which is economically acceptable It has been recognized that in rolling mill stands provided with a control arrangement which operates on the basis of the changes in the rolling pressure or expansion in order to obtain a rolling operation without tolerances, the effect of excentric rolls is actually increased. This is due to the fact that these control arrangements operate in the manner that upon an increase of the rolling pressure or frame elongation, a control magnitude is produced so as to reduce the rolling gap to the desired or nominal value and vice-versa. This procedure is correct only in the case where the changes are caused by the rolling stock itself such as from its varying thickness or its changing resistance to rolling or deformation. However, if the rolling pressure increases due to the excentricity of a roll it would be necessary to increase the rolling gap by the amount of the beat or excentricity of the roll in order that no groove or wave valley be pressed into the rolling stock. However, this prior art control arrangement even increases this effect by a closer positioning of the rolls upon an increase in the rolling pressure. The same is true for the reverse case where the beat of the roll is 180 from the rolling gap and a ridge or wave is produced in the rolled strip.

It is therefore an important feature of this invention to render ineffective the control magnitudes transmitted due to the excentricity of the rolls by erroneous signals, and to do so without impairing the ready operation of the control arrangement concerning the adjustment of the pressure effects derived from the rolling stock itself. It is therefore not sufiicient to switch the control arrangement periodically off and on in the frequency of the excentricity effect produced at the rolls, which, by the way, would only be possible in the case of a pinion drive of the rolls. But in the four-high stands in question the so called twin drive is customary. As the backup rolls have usually not exactly the same diameter, the twin drive exhibits therefore a change in the phase position of the excentricity of both rolls from one rotation to the next. This difficulty is also taken into account in the control arrangement of this invention.

It is a second feature of this invention to produce control magnitudes based on correct signs, besides cancelling control magnitudes based on erroneous signs, and of such a magnitude that the influence of excentric rolls is completely eliminated.

In view of prior art control systems of the type mentioned above, the present invention provides a process and apparatus for eliminating the effect of excentric rolls which comprises the following steps: the excentricity characteristics of each roll are registered in its travel symmetrically to the rolling path or plane; an algebraic sum is produced from the measured excentricity values which vary as a rule between a maximum and a minimum per rotation, that is to say the addition of the maximum value of one roll and the minimum value of the other roll would produce the sum zero; this sum, which is a measurement of the rolling gap changes due to excentricity of the rolls, is superimposed as disturbance value or factor upon the control system-if desired also with a reversal of the existing signin the sense that the control values of the control system which arise due to the excentricity of the rolls from the changes in the rolling pressure or due to expansion are compensated or balanced out. In spite of a change in the rolling pressure or expansion of the stand, the control system does not react in the same degree as it Would otherwise respond in the Wrong direction, because the changes in the rolling pres sure or due to expansion are also a function of the algebraic sum of the momentary values of the excentricity effects of both rolls that are active in the rolling gap. In the case of soft stands, for example, stands with thin stay bolts which may be made intentionally soft in connection with quick acting electro hydraulic control arrangements, the cancellation according to the invention of the control or adjustment values based on erroneous signs may already lead to satisfactory results. The changes of the rolling pressure due to excentricity of the rolls are in this case absorbed to a large extent by the expansions of the stand because in view of the cancellation of the control magnitudes according to this invention the soft stand is not controlled in this respect. This can thus lead to the following conclusion: the softer an uncontrolled rolling mill stand is, the less effect will the excentricity of the rolls have on the rolling stock. But such a soft stand reacts just as easily to a changing rolling or deformation resistance of the rolling stock. so that one sacrifices in this manner with the elimination of the infinence of excentric rolls an unquestionable exactness of the rolling operation. It is only in combination with a quick acting control arrangement and the process of this invention that a rolling stand is provided which, independent to a large extent from its own rigidity, provides a constant rolling gap-as far as varying properties of the rolling stock cause the controlling action-and which permits simultaneously a softness of the stand which absorbs the excentricity of the rolls.

The present invention also shows a way to adjust the excentricity of the rolls in a positive manner in order to eliminate also in existing rigid stands the influence of excentric rolls, or to produce in new structures the best possible effect from the start. As the disturbance value and the control or adjustment value to be compensated and having a wrong signal correspond in the absolute magnitude, and as both values are functions of the sum of the excentricities of both rolls active in the rolling gap,

it is merely necessary, according to the present invention, to increase the disturbance values to the double value required to compensate the periodically arising control or adjustment values. If the adjustment value is for example +1. the disturbance value is originally 1, in order to cancel the adjustment value. If the negative disturbance value is doubled to 2 the compensation produces a negative adjustment value of l, that is to say, the adjustment value which was originally correct in its order value, has now the correct sign. The product resulting from this process is a sheet or strip which is free of periodically arising thickened and thinned portions which are characteristic traces of the effect of excentric rolls.

A construction may be provided in which the exccntricity of the rolls during operation may be registered directly at the rolls, and relative to the insert members, appro riately at the edges of the roll surface or on the side. so that the deflection of the roll does not enter into the measured values. The unavoidable vibrations in the rolling mill operation as well as the emulsions adhering to the rolls would create substantial difficulties to a dependable measurement during a cold rolling operation in view of the roll beat of only a few hundreds of a millimeter. During hot rolling where the rolls are not ground as closely in view of the cost involved and where the excentricity may amount to several tenths of a millimeter, it is easier to measure the excentricity at the rolls themselves.

In order to eliminate these difficulties in measuring the excentricities, the invention provides an arrangement for carrying out the process according to this invention which includes a copying or scanning device installed separately from the rolling stand and provided with an indicator element or template associated with each roll and rotating synchronously therewith, and on which the excentricity of the rolls established beforehand on a grinding lathe. for example, are reproduced or set, and which are coupled in a phase position with the excentricity of the built-in rolls over electrically connected shafts or the like to the roll drive or the rolls, each indicator element cooperating with a scanner whose functional translation corresponds to the measurement of the excentricity of the rolls symmetrically to the rolling line, and in which a device for compiling the algebraic sum of the scanned values as well as a compensator are provided, in which the measuring. control or adjustment values on the one hand and the disturbance value derived from the summer on the other hand are connected in opposition or whereby the desired control value is regulated.

The various features and advantages of this invention will be apparent from a reading of the following description taken in connection with the attached drawings showing a four-high stand with an electrically operated hydraulic control arrangement responsive to rolling pressures to produce a constant tension in the roll stand or a constant rolling gap and in which:

FIG. 1 shows a four-high frame with the diagrammatic control arrangement and the scanning apparatus tracing the excentricity of the rolls and FIGS. 2 and 3 show two modifications of the scanning apparatus for transmitting the excentricity of a roll to a template subject to electronic scanning.

In reference to the drawing, FIGURE 1 shows a normal stand or frame having cast posts, and according to a known construction elastic pressure members 3 in the form of a diaphragm are arranged between the upper chuck 1 and the adjusting spindles 2 for providing a coarse adjustment. The pressure members 3 may be placed under tension by means of hydraulic expansion pistons 4 before commencing the rolling operation. The tension pressure is transmitted over pressure indicator boxes 5 into the posts 6 to put them also under a pretension.

A hydraulic pressure of high power is directed against expansion pistons 4 from pressure intensifier 8 through line 7. On the low-pressure side the pressure intensifier 8 is connected over line 9 to a control slide valve 10. The line 11 leads from slide valve 10 to a pressure source and line 12 is the return line. The piston rod 13 of the slide valve is regulated by conventional adjusting means (not shown} located in the regulator 14.

The measured pressure value of pressure measuring box 5 is introduced into regulator 14 through line 15. This value comprises the sum of the rolling pressure PR and the hydraulic tension force PHy of expansion piston 4. In principle, the regulation is directed to the constancy of the sum PR-t Ph'y, i.e. to the constancy of the tension in the elastic pressure members 3 and the stand posts 6. which amounts to a constant rolling gap. When the rolling pressure PR increases it is accordingly necessary that the hydraulic tension force PH or the specific pressure in the lines 7 be reduced. This control effect has the wrong sign in the case where the rolling pressure increases due to the excentricity of the rolls because in that case the value PHy would have to be increased or at least should not be decreased. The same problem exists also in the case of mechanically adjusted rolling stands where the rolls are set closer when the rolling pressure increases. However, in solving the problems of excentric rolls, an electriohydraulic control arrangement is preferable due to its shorter reaction time and because it is less sensitive to frequent operating changes.

A suitable copying device is shown in FIGURE 1 and is provided with electrically scanned indicator elements or templates. These elements consist of two excentric discs 35, 36 whose excentricity represents the excentricity or non-roundness of the rolls in an enlarged scale, and they rotate on electrically operated shafts 18, 19 synchronously and in a phase position corresponding with the excentricity of the rolls to which they are connected. A scanning device in the form of a differential transformer 37, 38 is associated with each excentric disc and the iron core 370, 38a respectively of each transformer 37, 38 is provided with a scanning roller 37!), 38b which is urged against the circumference of the concentric discs. The plane 39 which passes through the axes of rotation of excentric discs 35, 36 corresponds to the vertical rolling plane of the rolling stand. The two scanning rollers 37b, 38b engage the excentric discs symmetrically to the imaginary rolling line 40 but displaced in a direction opposite to the direction of rotation of the discs and in a common vertical plane 41. This displacement has the purpose of taking into account a longer response time of the compensation control with regard to a normal regulation of the roll stand.

Depending on the position of the scanning rollers or the iron cores 37a and 38a, the differential transformers 37 and 38 furnish at the secondary winding various voltages which may have different signs depending on whether a maximum or a minimum of excentrieity is present at a. scanning roller. The measured electrical values are transmitted over lines 42, 43 and over potentiometers 44, 45 to a summer 46 in which the algebraic sum of the scanning values is formed. This value is transmitted as disturbance value over an amplifier 47 and line 48 to a compensator 49 into which the values from the pressure measuring box 5 are conducted through line 15 in order to compensate these two measurement values before they enter the regulator 14 as far as any rolling pressure changes due to the excentricity of the rolls is concerned.

The operation of the scanning device according to FIG- URE 2 is as follows: after the positioning of one or both of the rolls whose excentricity has been determined previously and been indicated on the rolls, the excentricity of the discs 36, 35 is set in each instance to the same phase position relative to the excentricity of the corresponding roll before their shafts are coupled to the synchronous drive. It is necessary to take into account that the exeentricity of both rolls 16, 17 may be different, for example in roll 16 it may be only 3 mm. in contrast to the other roll 17 which may be mm. In order to take into account this difference in the excentricity or nonroundness of the respective rolls, one could insert after each roll grinding operation newly adapted excentric discs. But with the electrical scanning arrangement of the invention this is not necessary, because it is possible to carry out a uniform adaption of the scanning values in the ratio of the excentricity of the rolls by means of the p0 tentiometers 44 and 45. These potentiometers are so regulated that at the voltage meters 50 and 51 voltage values of a ratio of 2:5 may be read. The position of discs 35, 36 is selective except that their excentricity-as shown must have the same phase position relative to each other. For this reason the scanning device is appropriately adjusted before the excentric discs are coupled to the drive in phase position with the respective rolls when their phase position is different.

The amount of beat or excentricity of the rolls may be different during operation in the rolling mill, that is to say during loading of the rolls, from what it was before on the grinding lathe measured with a test watch. There may be tensions in the rolls which disappear after a few rotations. In order to determine this, one can start the drive of mutually adjusted work rollers, regulate the amplifier 47 to non-amplified transmission of the disturbance value, and test if the measuring device 52 indicates pressure variations in the line 7. If this is the case, the electrical scanning device is not balanced properly, or the excentricities of the rolls have changed under load. By rotating potentiometers 44, 45 it is possible to adjust the scanning device in such a way that the measuring device 52 does not indicate any pressure variations. This adjusting process is carried out best when the rolls are positioned with their excentricities in the same phase, because only the largest and most easily recognizable excentricities appear at the measuring device 52 when the balance is not correct.

With this the compensation adjustment is still not set to the best possible effect as only the major values are cancelled from the stand adjustment in order that the rolls do not move closer when the excentricity 16a and 17a come into the area of the rolling gap. However, the elastic pressure members 3 have a favorable effect in this respect because they make the roll stand soft, so that the upper roller 16 may move upwardly as the excentric areas of the rolls approach.

The best possible effect is obtained when the rolls are pressed apart in the rolling gap by the expansion pistons 4 corresponding to the sum of their excentricity. For this purpose amplifier 47 is regulated to about double amplification. The disturbance value passing through line 48 to compensator 49 is then oppositely twice as large as the measured value of the rolling pressure in line to be cancelled, so that as difference a value corresponding to the rolling pressure with a reversed sign enters the regulator 14. With an increase in the rolling pressure a pressure increase will take place also in line 7, which produces the desired result. In the case Where the measuring devices 52 and 53 are suitable to indicate pressure forces, the cornpensation of the excentricity of the rolls is complete during the trial run of the rolling stand without load when the deflections of the two indicators move always in the same direction and are equal. During operation of the rolling stand control values which are derived from the rolling stock may be superimposed on the compensation control, so that the movement of the indicator hands of the measuring devices 52 and 53 give an indication for regulating the excentricity of the rolls only from time to time, when the excentricities are of. equal phase and their influence is at a maximum. Instead of cancelling the measured value it is possible to connect the electrical disturbance value also against the control value or the adjusting value in the regulator 14, or it may serve to regulate the control-nominal value. A variation of the regulation setting by changing the nominal value amounts to a change of the roll gap.

Referring now to FIGURES 2 and 3, it will be seen that they illustrate two possibilities of adjusting the excentricity of the rolls with respect to indicator devices of a special type. The polished roller 54 which is mounted in the roller pins, is scanned, while being rotated, by means of a testing watch 55, before it is built into the stand. The testing watch produces a measuring current corresponding to the deflections of the watch hand, and these currents are fed, as seen in FIGURE 1, to a recording instrument having a rotating disc 56. The roll and the disc rotate synchronously. The recording stylus shows virtually the cross-section through the roll in the perpendicular scanning plane of the roll by the line 57, which illustrates thus an excentricity. The disc 56 may be employed directly as an indicator element in a scanning device in that the line 57 is scanned photoelectrically or magnetically when the stylus is suitably constructed.

In the modification of the excentricity recording device illustrated in FIGURE 3 the measuring circuits travel from the measuring clock 55 to a mixer stage 58 into which a sound frequency is introduced at 59. The mixer frequency is transcribed onto an endless tape 60 in which one rotation corresponds to one or to a multiple of the rotation of the roll. The tape is provided like a film tape with perforations into which the teeth of the driving discs 61 and 62 penetrate and represents also an indicator or template for a scanning device from which the excentricity of a roll may be registered through a magnetic head. Instead of a magnetic tape an illuminated film strip may be used as indicator or template element. in which case the scanning devices would operate in an electro-optical manner. The modified copying or scanning devices illustrated in FIGURES 2 and 3 do not present any difficulties in their construction, as only known elements and known electronic circuits are employed, and for this reason a detailed showing of the electronic system of such copying devices is not made here.

The invention is applicable independently of whether the rolling stand has been given a soft construction due to the presence of a rapidly responding control arrangement or not. Although the necessity for eliminating the effect of excentric rolls in pressure regulated roll stands is particularly obvious, it is within the scope of this invention to apply the compensation adjustment also in stands which are not adjusted at all, or which are adjusted by means of thickness measuring devices. In such cases it is not necessary to compensate or overconipensate an input or output value of a control arrangement, but the disturbance value which has not been doubled, that is to say the signal obtained by any means, which is proportional to the given algebraic sum of the excentricity of the rollers, is conducted as control value to the adjusting motors, or to any type of hydraulic adjusting device, under certain circumstances also to a device for equalizing the weight of the rolls, which must be designed to allow a periodically controlled elongation of the stand corresponding to the cxcentricity, in order to regulate the distance of the roll axes inversely to the rolling gap changes to be expected from the excentricity of the rolls.

What is claimed is:

1. Apparatus for eliminating the effect of excentric rolls in hot and cold rolling mills for metal sheets and strips comprising in combination support means for said rolls,

tensioning means for said support means,

fluid means for pressurizing said tensioning means to adjust the gap between said rolls,

means for registering the tension value of said support means,

means for registering the excentricity value of said rolls,

compensating means for balancing said tension value and said excentricity value to produce a control value,

means for feeding said tension value and said excentricity value to said compensating means,

and regulating means for receiving said control value to regulate the flow of said fluid means to said tensioning means to adust the rolling gap.

2. Apparatus for eliminating the effect of excentric rolls in hot and cold rolling mills for metal sheets and strips comprising in combination support means for said rolls,

fluid operated piston means for tensioning said support means to adjust the rolling gap,

fluid pressure means for pressurizing said piston means,

means for registering the tension value of said support means,

means for registering the excentricity value of said rolls,

compensating means for balancing said tension value and said excentricity value to produce a control value,

transfer means for feeding said tension value and said excentricity value to said compensating means, valve means for adjusting the flow of said fluid pressure means,

and regulator means connected to said compensating means and said valve means,

said regulator means actuating said valve means in response to said control value received from said compensating means.

3. Apparatus for eliminating the effect of excentric rollers in hot and cold rolling mills for metal sheets and strips comprising in combination support means for said rolls,

fluid operated pistons for tensioning said support means to adjust the rolling gap,

fluid pressure means for pressurizing said pistons,

means for registering the tension value of said support means,

means for registering the excentricity value of said rolls, said excentricity registering means including (a) template means rotating synchronously with said rolls and coupled thereto in a phase position corresponding to the excentricity of said rolls,

(b) scanning means associated with each template means for registering the excentricity of said rolls symmetrically to the rolling plane,

(c) summer means for compiling the algebraic sum of the values collected by said scanning means,

compensating means for balancing said tension value and said excentricity value to produce a control value,

transfer means for feeding said tension value and said excentricity value to said compensating means,

slide valve means for adjusting the flow of said fluid pressure means,

and regulator means connected to said compensating means and to said valve means,

said regulator means actuating said valve means in response to said control value received from said compensating means.

4. The apparatus according to claim 3 wherein said template means are excentric discs.

5. The apparatus according to claim 3 wherein each scanning means is connected to a transformer and wherein a potentiometer is connected between said transformer and said summer means.

6. The apparatus according to claim 3 wherein a variable amplifier is connected between said summer means and said compensating means.

7. The apparatus according to claim 2 wherein said excentricity registering means include an excentricity measuring instrument connected to each roll and adapted to generate an electric current,

and a recording device having a disc rotatable synchronously with the roll. to indicate its excentricity.

8. The apparatus according to claim 2 wherein said registering means include an excentricity measuring instrument connected to each roll and adapted to generate an electric current,

a mixer device connected to said measuring instrument and receiving a sound frequency,

a recording head connected to said mixer device, and

a recorder device adapted to receive the mixer frequency from said recording head.

9. A process for eliminating the effect of excentric rolls in hot and cold rolling mills for metal sheets and strips comprising producing a signal proportional to the algebraic sum of the excentric values of said rolls,

conducting said signal to a compensating device to balance the signal representing the tension values of the roll support means received in said device,

and transmitting the mixed signals as control signal to a regulator for adjusting the tension in said roll support means.

10. The process according to claim 9 wherein the signal representing the excentricity values is increased to double the value necessary to compensate the signal representing the tension values of said support means.

11. The process according to claim 9 wherein the distance of the roll axes is adjusted inversely to the rolling gap corresponding to the excentricity of the rolls.

References Cited UNITED STATES PATENTS 3,049,950 9/1958 Pearson 72-8 CHARLES W. LANHAM, Primary Examiner.

R. D. GREFE, Assistant Examiner. 

1. APPARATUS FOR ELIMINATING THE EFFECT OF EXCENTRIC ROLLS IN HOT AND COLD ROLLING MILLS FOR METAL SHEETS AND STRIPS COMPRISING IN COMBINATION SUPPORT MEANS FOR SAID ROLLS, TENSIONING MEANS FOR SAID SUPPORT MEANS, FLUID MEANS FOR PRESSURIZING SAID TENSIONING MEANS TO ADJUST THE GAP BETWEEN SAID ROLLS, MEANS FOR REGISTERING THE TENSION VALUE OF SAID SUPPORT MEANS, MEANS FOR REGISTERING THE EXCENTRICITY VALUE OF SAID ROLLS, COMPENSATING MEANS FOR BALANCING SAID TENSION VALUE AND SAID EXCENTRICITY VALUE TO PRODUCE A CONTROL VALUE, 